1. Field of the Invention
The present invention relates to an arrangement structure of a shifting actuator for drivingly shift-switching a multistage transmission attached to an internal combustion engine mounted on a motorcycle.
The multistage transmission includes a plurality of drive gears and driven gears which are rotatably supported by respective parallel gear shafts in a constant-mesh state for each speed-change stage.
2. Description of Background Art
In general an internal combustion engine mounted on a motorcycle is provided integrally with a multistage transmission in an engine case. A space is narrow where such an engine is mounted on a body frame. If auxiliaries are arranged around the engine, the space is increasingly narrowed. In addition, also a shifting actuator for drivingly shift-switching the transmission has to be arranged so as not to interfere with the auxiliaries.
The shifting actuator is a relatively large actuator, which is usually provided so as to project. Therefore, it is not easy for the shifting actuator to be arranged because of being restricted by the auxiliaries.
There is an example in which an internal combustion engine mounted on a motorcycle has a transmission integral with an engine case (a crankcase) and a shifting transmission for drivingly shift-switching the transmission is provided on the engine case so as to project therefrom (see e.g. Japanese Patent Laid-open No. 2008-137417)
In Japanese Patent Laid-open No. 2008-137417, an electric motor which is the shifting actuator is projectingly provided at a left lateral lower portion, not interfering with auxiliaries, of the engine case provided integrally with a transmission.
Since the shifting actuator disclosed in Japanese Patent Laid-open No. 2008-137417 is projectingly provided at a left lateral lower portion of the engine case, it is not necessary to allow the actuator to have a special structure. However, the laterally projecting actuator is not preferable in view of external appearance.
In addition, a protecting member or the like has to be especially provided to protect the shifting actuator from collision with a foreign object such as a flying stone.
The electric motor which is the shifting motor disclosed in Japanese Patent Laid-open No. 2008-137417 is mounted to a gear shift device projectingly provided on the left lateral lower portion of the engine case.
The gear shift device is a transmission mechanism configured such that relay gears, a worm-like barrel cam and a pin gear are engaged with one another to transmit the drive of an electric motor. Such a gear shift device is projectingly provided and the electric motor is mounted to this gear shift device.
In Japanese Patent Laid-open No. 2008-137417 described above, not only the shifting actuator for turning a shift drum inside the engine case but also the transmission mechanism is provided to project outwardly from the engine case. Thus, the gear shift device of the transmission mechanism is complicated and an attachment structure in which the gear shift device is mounted to the engine case with sealing ensured is also complicated, so that also mounting work is not simple.
Additionally, the shifting actuator and the transmission mechanism are mounted to the engine case to project externally therefrom, that is, the whole is exposed, which is not preferable in view of external appearance.
Further, a protecting member or the like has to be especially provided to protect the shifting actuator and the transmission mechanism from collision with a foreign object such as a flying stone, etc.
This constant-mesh type multistage transmission is such that one of the drive gears and driven gears is secured to a gear shaft and the other is rotatably supported by another gear shaft and a gear to be engaged with the gear shaft is switched from the rotatable gears by an engagement switching mechanism for executing shifting.
Japanese Patent Application No. 2008-93703 which has previously been filed by the same Applicants discloses a shift drive mechanism that drives an engagement switching mechanism to switch engaging means for executing shifting. The engaging means is provided between a plurality of gears and a gear shaft to execute engagement therebetween. This shift drive mechanism is configured as below. A shift rod disposed at the hollow central axis of the gear shaft moves cam rods in an axially movable and slidable contact with the hollow inner circumferential surface of the gear shaft. In addition, such cam rods drive the engaging means to execute shifting.
The multistage transmission disclosed in Japanese Patent Application No. 2008-93703 is configured as below. Gear trains composed of drive gears and driven gears meshing each other are housed in a transmission chamber defined in a crankcase. A plurality of the drive gears are secured to a drive gear shaft and a clutch is attached to a right end portion of the drive gear shaft passing through the right lateral wall of the crankcase.
The driven gear shaft is provided with an engagement switching mechanism provided with cam rods adapted to switch engagement between the driven gear shaft and each of the driven gears. An output sprocket is fitted to the left end portion of the driven gear shaft passing through a left lateral wall of the crankcase.
A shift rod insertably fitted into the driven gear shaft along a hollow central axis moves the cam rod.
The shift rod further projects leftward from the left end portion of the driven gear shaft passing through the left lateral wall of the crankcase. A shift rod movement mechanism in which a shift drum moves a guide pin provided at the left end portion of the shift rod is installed on the outside of the left lateral wall of the crankcase.
In short, the multistage transmission of Japanese Patent Application No. 2008-93703 has the clutch projectingly provided on the right of the crankcase and the shift rod movement mechanism provided on the left side of the crankcase. Therefore, the multistage transmission is increased in left-right (axial) width and enlarged.
This constant-mesh type multistage transmission is such that one of the drive gears and driven gears is secured to a gear shaft and the other is rotatably supported by another gear shaft and a gear to be engaged with the gear shaft is switched from the rotatable gears by an engagement switching mechanism for executing shifting.
In addition, Japanese Patent Application No. 2008-246752 which has previously been filed by the same Applicants discloses a shift drive mechanism that drives an engagement switching mechanism to switch engaging means for executing shifting. The engaging means is provided between a plurality of gears and a gear shaft to execute engagement therebetween. This shift drive mechanism is configured as below. A shift rod disposed at the hollow central axis of the gear shaft moves cam rods in an axially movable and slidable contact with the hollow inner circumferential surface of the gear shaft. In addition, such cam rods drive the engaging means to execute shifting.
The shift drive mechanism of the multistage transmission disclosed in Japanese Patent Application No. 2008-246752 is configured as below. A shift pin radially passes through a cylindrical operating member mounted to an end portion of the shift rod via a bearing. One end of the shift pin passing therethrough is slidably fitted to a groove formed to extend in the axial direction of the guide member. The other end of the shift pin is slidably engaged with a shift guide groove formed in the outer circumferential surface of a shift drum. The shift drum is turned to axially move the shift pin guided by the shift guide groove. In this way, the shift rod is moved via the cylindrical operating member. Shifting is executed by the engagement switching mechanism operated by the movement of the shift rod.
The shift pin undergoes an operating force resulting from the turning of the shift drum at an end portion engaged with the shift guide groove to be parallel-moved in an axial direction. However, an end portion on the side opposite the end portion engaged with the shift guide groove slides along the groove formed to extend in the axial direction of the guide member. Therefore, the end portion of the shift pin on the side opposite the end undergoing the operating force causes friction resistance. Thus, the shift pin is configured to tilt easily in the axial direction.
The shift pin may not be parallel-moved with its posture maintained due to the inclination and if so, the friction resistance will increase to make the smooth axial movement difficult.
The present invention has been made in view of such situations and it is an object of the present invention to provide an arrangement structure of a shifting actuator of an internal combustion engine mounted on a motorcycle, in which while the shifting actuator is provided externally of an engine case of the engine so as not to interfere with auxiliaries, it is protected from collision with a foreign object without external protrusion and external appearance is kept satisfactory.
It is also an object of the present invention to provide an attachment structure of a shifting actuator of an internal combustion engine mounted on a motorcycle, in which the attachment structure of the shifting actuator to an engine case is simple, attachment work is easy, the shifting actuator can be prevented from collision with a foreign object, and external appearance can be kept satisfactory.
It is a further object of the present invention to provide a multistage transmission that can reduce its axial width to achieve compactness.